1. Technical Field
Embodiments of the present disclosure relate to circuits for setting reference voltages and semiconductor devices including the same.
2. Related Art
In general, an integrated circuit (IC) such as a semiconductor IC may include a semiconductor system that receives external signals supplied from an external system to generate internal signals. The semiconductor system may compare the external signals with a reference voltage and may buffer the external signals to generate internal signals used in internal circuits of the semiconductor system. The internal signals may set logic levels based on results of comparisons of the external signals and the reference voltage. For example, the internal signal may be set to a logic “high” level if a voltage level of the internal signal is higher than the reference voltage, and the internal signal may be set to a logic “low” level if a voltage level of the internal signal is lower than the reference voltage. The reference voltage inputted to the semiconductor system may have an intermediate level between a predetermined maximum level (VILmax) and a predetermined minimum level (VILmin). However, a level of the reference voltage may fluctuate according to an environmental condition, noises of power signals of a system, shapes of interconnection lines of a printed circuit board (PCB), and/or shapes of interconnection lines of a package. If a level of the reference voltage fluctuates, the semiconductor system may incorrectly recognize levels of the external signals and thus may generate internal signals having incorrect logic levels which may cause a malfunction of the internal circuits. Thus, it may be important to verify and confirm the reference voltage level so that the semiconductor system receives the external signals correctly.
Recently, a command bus training (CBT) scheme for finding a range of a level of the reference voltage and for setting a level of the reference voltage has been widely used in an initialization operation such as a booting operation of a semiconductor device to enable the semiconductor device to operate normally.